Benzylidene sorbitol compounds that are used as a clarifying agent for improving the clarity of a polyolefin-based resin have a high melting point and a low solubility to solvents; therefore, during chemical synthesis, precipitation of crystals occurs simultaneously with the reaction. These crystals are highly cohesive whisker-form crystals and, since powder thereof obtained through a pulverization process has a low bulk specific gravity and is compressible, the power has poor fluidity and automatic measurement thereof is difficult.
One example of a method of supplying an additive to a polyolefin-based resin is a method of feeding an additive from a hopper to a processing machine, such as an extruder, to which a polyolefin-based resin has been loaded; however, when a benzylidene sorbitol compound is fed from a hopper, the compound may induce blocking in the hopper, resulting in defective loading.
Further, a clarifying agent requires to be uniformly dispersed for expression of its function; therefore, in many cases, the clarifying agent is added to a processing machine in the form of master powder prepared in advance by blending the clarifying agent with a certain amount of a polyolefin-based resin. A clarifying agent having a low bulk specific gravity causes layer separation during the preparation of master powder and uniform blending cannot thus be achieved, so that defective molding may occur and the resulting molded article may not have stable physical properties.
As solutions to such problems, for example, Patent Document 1 proposes an additive composition obtained by mixing a benzylidene sorbitol compound with a submicron-sized silica compound. Patent Document 2 proposes a clarifying agent composition which is a mixture of a dibenzylidene sorbitol compound having a volume particle size, D97, of 30 μm to 200 μm and tetrakis[3(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxymethyl]methane. Further, Patent Document 3 proposes a crystal nucleating agent composition for polyolefin-based resins, which comprises 1,3:2,4-bis(3′,4′-dimethylbenzylidene)sorbitol, a metal phosphate and a compound that is a monovalent metal salt of fatty acid optionally substituted with a hydroxy group.